Refrigerants have been in widespread use for over fifty years. In the past decades, the deleterious effects of the refrigerants on the environment have become apparent. Most widely discussed has been the depletion of the earth's ozone layer caused by chemical reactions between ozone and refrigerants such as freon and other chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs).
The industry is addressing these concerns by reformulation of refrigerants to reduce their damaging effects. However, there exist millions of tons of harmful refrigerants still in use. Automobile air conditioning units and refrigerators are but two of the most common uses.
To address this latent threat, the US Environmental Protection Agency (EPA) has implemented regulations concerning recovery of used refrigerants when equipment is recharged, repaired or decommissioned. Among other requirements, these standards require that refrigerants be evacuated from such systems to specified vacuum pressures, the specific pressure depending on the type of equipment and the specific refrigerant involved.
The technology for evacuating refrigerants is well developed. In the patent literature, the technology can be traced back at least thirty years (see, for example, U.S. Pat. No. 3,232,070). With onset of EPA regulation, the past decade has seen a storm of developments (see, for example, U.S. Pat. Nos. 4,285,206, 4,646,527, 4,768,347, 4,809,520, 4,856,290, 4,938,031, 5,033,271, 5,038,578, 5,097,667, 5,157,936, and 5,161,385).
Despite the massive research and development that has taken place, all of the prior art systems known to the applicants share a common failing: they are ill-suited to cope with refrigerants that may be encountered in either the liquid or gas phase.
Most prior art systems capable of evacuating both liquids and gases followed one of two approaches. The first integrates two evacuation circuits into a single apparatus, one circuit tailored for handling liquid, the other tailored for handling gas. The second employs means (often an evaporator) for converting the incoming refrigerant to a desired phase, and provides a single evacuation circuit tailored to handling that phase. It will be recognized that both of these approaches suffer by reason of increased cost, complexity, weight and size, and reduced reliability.
In accordance with the present invention, refrigerant is recovered using a single pump unit, regardless of the refrigerant's phase. This feat is achieved by sensing the phase of the refrigerant and changing the pump's operation accordingly. The refrigerant phase can be sensed by a temperature-responsive element, such as a thermistor, or by other phase-sensing technology.
In a preferred embodiment, the pump unit is a vane pump whose rotational speed is changed in response to the refrigerant's phase. If liquid refrigerant is sensed, the pump operates at a lower speed. If gas refrigerant is sensed, the pump operates at a higher speed. The two speeds are chosen so that the pump will draw an EPA-specified vacuum on the refrigerant present.
In other vane-pump embodiments, the pump's operation is changed by changing the pump's mechanical configuration, rather than its rotational speed.
In one embodiment of the invention, the pump and its associated motor are integrated into a single assembly that obviates the need for dynamic bearing seals.
The foregoing and additional features and advantages of the present invention will be more readily apparent from the following detailed description thereof, which proceeds with reference to the accompanying drawings.